We all know that stabled horses should have as much access to long forage as possible. The trouble is forage is dusty and when horses nuzzle through it and pull mouthfuls from hay nets, the particles become airborne, are inhaled and can quickly cause coughing.

The problematic particles are the extremely small (<5µm) fungal spores (notably Aspergillus spp (2–4 µm)), and heat-loving bacteria (Thermoactinomyces vulgaris and Saccharopolyspora rectivirgula) which penetrate deep into the lungs and can cause allergenic respiratory problems.

As the respiratory system of the horse cannot be improved by training and is the performance limiting step in hard-working horses, it is paramount that we keep the lungs in a healthy condition by reducing dust in the stable environment.

This is best achieved by using low-dust bedding and removing dust from the forage by using suitable pre-feeding treatments.

Removing dust from the environment

The positive impact of removing dust from the environment on horse respiratory health has recently been demonstrated by Dauvillier and van Erck-Westergren, (2016). They collected data in Belgium, France and the Netherlands from 482 horses with respiratory issues and showed that feeding steamed hay, i.e., hay that had been high-temperature steamed in a Haygain steamer, reduced the risk of inflammatory airway disease by 63%. Furthermore this study showed that steamed hay had the lowest risk of diagnosing fungi in the lungs compared with when soaked hay or haylage was fed.

When looking at the results detailed in Table 1 below, it is clear that low dust regimes are effective at removing dust from the stable environment. Furthermore these results (published in 2017) show the negative impact straw and dry hay can have on dust levels in both the breathing zone and general stable zone, particularly in American Barns.

Table 1. Airborne respirable dust / l air in the breathing zone (BZ) and general stable zone (SZ) in American Barn and single stables under four management regimes (12).

American Barn

Single stables

SZ

BZ

sig

SZ

BZ

Sig

Steamed hay + shavings

325

300

1.00

270

360

0.219

Dry hay + shavings

522

827

0.008

509

637

0.021

Haylage + straw

972

517

0.001

2912

533

0.001

Dry hay + straw

6250

5079

0.382

2901

943

0.234

Healthy lungs by reducing airborne respirable dust in forage

The results from 4 separate experiments are shown in Figure 1 and demonstrate the importance of full steam penetration into the hay. Steaming using a Haygain steamer reduces airborne respirable dust (ARD) by 99% producing clean forage that remains clean for at least 24 hours after steaming. Steaming hay using a home-made bin or pouring a kettle of hot water over the hay does not reach the necessary high temperatures, nor does it distribute the steam throughout the hay, so these methods are only partially effective at reducing ARD.

Figure 1

Healthy guts by reducing bacteria and mould in forage

The Experiment 5 above measured a particular fungi called Aspergillus spp, one of the known allergens in hay, showing a 95% reduction from steaming with a Haygain (HG). Figure 2 below is a summary of 6 different experiments where the bacteria and mould contents of hay were determined after various different wetting treatments. All experiments that examined the effect of soaking or partial steaming (bin or kettle) on bacteria showed worrying increases and compromises the hygienic quality of the hay. Steaming haylage with a Haygain steamer (Experiment 8) was highly effective and had the added bonus of increasing shelf-life with fungi and bacteria contents lower 4 days after opening than in freshly opened haylage.

Figure 2

As some owners soak hay to reduce sugar content for their laminitic horses and ponies, study 9 examined the effect of various different wetting and steaming combinations on bacteria and water soluble carbohydrate (WSC) contents in 5 different UK hay types. All the wetting treatments were effective at reducing WSC with an average of 35% decrease, but the range was highly variable, ranging from 2 – 54%, so not a reliable way of reducing WSC in hay. Results for bacteria contamination post steaming, soaking and combinations of soaking and steaming confirmed the highly beneficial effects of steaming in that soaking increased bacteria content by 5 times whereas steaming even after soaking reduced bacteria by 99%.

Treat it and eat it = happy horse

30 samples of hay from across the UK were analysed (13) for nutrient content when dry and after high-temperature steaming in a Haygain steamer. All nutrients were unaffected by steaming except WSC which dropped on average by 18% although the range was similar to that noted for soaking of between 2-50%.

Two studies examined the palatability of steamed hay versus, soaked hay or haylage(14,15) and found that horses chose to eat the steamed hay first and also ate more of it. Kentucky Equine Research (16) performed a full 12 week feeding trial where voluntary forage intake and digestibility were measured for dry, steamed and soaked hay. Their findings on palatability agreed with the previous experiments and found that despite the 4% loss of WSC from steamed hay and the 9% from soaked hay and the proportional increase in fibre content /kg (due to loss of WSC) the digestibility was similar across all treatments, thus steaming hay improves palatability and does not compromise digestibility.

References

Dauvillier, J., and van Westergren, E. (2016) The Prevalence of Fungi in Respiratory Samples of Horses with Inflammatory Disease ACVIM June 2016

Stockdale, C and Moore-Colyer, M.J.S (2010) Steaming hay for horses: The effect of three different treatments on the respirable particle numbers in hay treated in the Haygain steamer. European Workshop for Equine Nutrition, Cirencester, Sept 2010. The Impact of nutrition on the health and welfare of horses. EAAP publication No. 128. Ed Ellis, A., Longland, A.C., Coenen, M and Miraglia, N. p136-138

Moore-Colyer, M.J.S and Fillery, B.G. (2012) The Effect of three different treatments on the respirable particle content, total viable count and mould concentrations in hay for horses. 6thEuropean Workshop for Equine Nutrition, Lisbon, Portugal, June. 101-106.

James, R. and Moore-Colyer, M.J.S. (2010) The effect of steam treatment on the total viable count, mould and yeast numbers in hay using the Haygain steamer European Workshop for Equine Nutrition, Cirencester, Sept 2010. The Impact of nutrition on the health and welfare of horses. EAAP publication No. 128. Ed Ellis, A., Longland, A.C., Coenen, M and Miraglia, N.p 128-132

Moore-Colyer, M.J.S and Fillery, B.G. (2012) The Effect of three different treatments on the respirable particle content, total viable count and mould concentrations in hay for horses. 6thEuropean Workshop for Equine Nutrition, Lisbon, Portugal, June. 101-106.

Leggatt, P. and Moore-Colyer, M.J.S (2013). The effect of steam treatment on the bacteria yeast and mould concentrations in haylage for horses. Proceedings of British Society of Animal Science Conference, Nottingham April 2013. p 103

Moore-Colyer MJS, Lumbis K, Longland AC, Harris PA. (2014).The effect of five different wetting treatments on the water soluble carbohydrate content and microbial concentration in hay for horses. Plos One.

James, R. and Moore-Colyer, M.J.S. (2013) Hay for horses: The nutrient content of hay before and after steam treatment in a commercial hay steamer. Proceedings of British Society of Animal Science Conference, Nottingham April 2013.